Well Australia is looking at 4 additional (2 yes and 2 maybe) and NZ is possibly looking at 2.IIRC the total number of whitetails started at 10. It was going to be 13, but LM cancelled the last three just before long lead items were bought, because of lack of orders for the 10 already building.
So, all new sales (including to Australia) have to add up to no more than 10.
IMO is pays to go big. There is really no mission where a single C-130 flying out of NZ is going to be cheaper, because you will have to fly multiple flights. Future equipment will get bigger and heavier (perhaps C17 only compatable), distances aren't getting any smaller.The C-130 size is no longer the best fit IMO.
C27J is now your small tactical, and C-17 is your everything. C-130 is down to niche stuff.
C17 plugs into US, AUS, UK chains and support. Between us having 10-12 C-17s is pretty significant. It wouldn't mean they would have to be based in OZ at all. But when 1 is down for maintenance, capability could easily be covered by the other nation. Its more about maintenance scheduling and planning that they would have to be based/operating in OZ.
Looks like a C17 could do Christchurch to McMurdo and back without refueling, just. Assuming a light load going down (some people, a few light pallets) and empty coming back. Certainly airdrops seem possible.